LCLS Conceptual Design Report - Stanford Synchrotron Radiation ...

L C L S C O N C E P T U A L D E S I G N R E P O R T
8.4.1 Characterization of Magnet Blocks with Helmholtz Coils................................... 8-16
8.4.2 Characterization of Magnet Blocks with Half-Period Fixture ............................. 8-18
8.4.3 LCLS Prototype Undulator Segment ................................................................... 8-20
8.5 Magnetic Design for the Undulator ................................................................................. 8-20
8.5.1 Choice of Magnet Material .................................................................................. 8-20
8.5.2 Undulator Magnetic Model .................................................................................. 8-22
8.5.2.1 Two-Dimensional Model..................................................................... 8-22
8.5.2.2 Three-Dimensional Model................................................................... 8-24
8.5.3 Undulator Segment Ends...................................................................................... 8-27
8.6 Mechanical Design .......................................................................................................... 8-27
8.6.1 Design of Magnetic Structure .............................................................................. 8-27
8.6.2 Provisions for Magnetic Tuning........................................................................... 8-33
8.6.3 Undulator Supports and Movers .......................................................................... 8-36
8.6.4 Thermal Considerations ....................................................................................... 8-37
8.7 Permanent Magnet Quadrupoles...................................................................................... 8-37
8.7.1 Quadrupole Mechanical Design ........................................................................... 8-38
8.8 Vacuum Chamber ............................................................................................................ 8-39
8.8.1 Electron Beam Collimation and Vacuum Chamber Design................................. 8-40
8.8.1.1 Beam Parameters Used in These Calculations..................................... 8-40
8.8.1.2 Permanent Magnet Material................................................................. 8-40
8.8.1.3 Undulator Vacuum Chamber ............................................................... 8-42
8.8.1.4 Beam Strikes at the Entrance to the Vacuum Chamber ....................... 8-42
8.8.1.5 Beam Strikes Inside the Undulator ...................................................... 8-43
8.8.1.6 Adjustable Collimators to Protect Undulator and Vacuum Chamber.. 8-45
8.8.1.7 Fixed Aperture Protection Collimators................................................ 8-46
8.8.1.8 Vacuum Chamber Surface Roughness................................................. 8-46
8.8.2 Vacuum System Requirements and Description .................................................. 8-47
8.8.3 Gas Load and Vacuum Pressure........................................................................... 8-49
8.8.4 Thermal Considerations ....................................................................................... 8-52
8.9 Wakefield Effects in the Undulator ................................................................................. 8-52
8.9.1 Introduction.......................................................................................................... 8-52
8.9.2 Wakefield Induced Beam Degradation ................................................................ 8-53
8.9.3 The Resistive Wall Wakefields ............................................................................ 8-54
8.9.4 The Effect of Flange Gaps, Pumping Slots, and Bellows .................................... 8-56
8.9.5 The Effect of Wall Surface Roughness................................................................ 8-57
8.10 Ion Effects ....................................................................................................................... 8-62
8.10.1 Introduction.......................................................................................................... 8-62
8.10.2 Ionization Processes ............................................................................................. 8-62
8.10.2.1 Ionization by the beam......................................................................... 8-62
8.10.2.2 Ionization by incoherent synchrotron radiation. .................................. 8-62
8.10.2.3 Tunneling ionization in the coherent laser field. ................................. 8-63
8.10.3 Emittance Dilution ............................................................................................... 8-64
8.10.4 Conclusion............................................................................................................ 8-65
8.11 Electron Beam Diagnostics.............................................................................................. 8-65
T A B L E O F C O N T E N T S